# lamellar

Lyotropic lamellar phase with uniform SLD and random distribution

Parameter Description Units Default value
scale Source intensity None 1
background Source background cm-1 0.001
thickness total layer thickness 50
sld Layer scattering length density 10-6-2 1
sld_solvent Solvent scattering length density 10-6-2 6

The returned value is scaled to units of cm-1 sr-1, absolute scale.

Polydispersity in the bilayer thickness can be applied from the GUI.

Definition

The scattering intensity $$I(q)$$ for dilute, randomly oriented, “infinitely large” sheets or lamellae is

$I(q) = \text{scale}\frac{2\pi P(q)}{q^2\delta} + \text{background}$

The form factor is

$P(q) = \frac{2\Delta\rho^2}{q^2}(1-\cos(q\delta)) = \frac{4\Delta\rho^2}{q^2}\sin^2\left(\frac{q\delta}{2}\right)$

where $$\delta$$ is the total layer thickness and $$\Delta\rho$$ is the scattering length density difference.

This is the limiting form for a spherical shell of infinitely large radius. Note that the division by $$\delta$$ means that $$scale$$ in sasview is the volume fraction of sheet, $$\phi = S\delta$$ where $$S$$ is the area of sheet per unit volume. $$S$$ is half the Porod surface area per unit volume of a thicker layer (as that would include both faces of the sheet).

The 2D scattering intensity is calculated in the same way as 1D, where the $$q$$ vector is defined as

$q = \sqrt{q_x^2 + q_y^2}$

References

F Nallet, R Laversanne, and D Roux, J. Phys. II France, 3, (1993) 487-502

also in J. Phys. Chem. B, 105, (2001) 11081-11088